In ATM switching facilities (ATM =Asynchronous Transfer Mode) it is frequently necessary to switch data packets (also referred to as "cells") from several input lines to one and the same output line. This is one of the reasons why data packets are temporarily stored there before, during, or after the switching process. The temporary storage may be in the form of several parallel queues. The queues are treated differently, so that the data packets are served differently according to which queue they belong to.
The invention is based on a facility as is described on pages 162 and 163 of an article entitled "Das ATM-Koppelfeld von Alcatel und seine Eigenschaften", which was published in "Elektrisches Nachrichtenwesen", Vol. 64, No. 2/3, 1990, a technical journal of Alcatel.
This facility forms part of an integrated switching element for ATM data packets (referred to as "ATM cells" or "cells"). In this facility, data packets which come from different inlets are allocated to several queues and temporarily stored there.
The facility comprises a memory device, a routing logic, and a memory management device.
The memory device contains several logic queues. "Logic" in this connection means that the assignment of memory cells to a queue is not permanent, but variable.
The routing logic allocates incoming data packets to one of the logic queues on the basis of routing information contained in the data packets.
The memory management device manages the locations of the memory device. It ensures the queue discipline in the logic queues and allocates vacant locations to the data packets to be inserted into the queues.
This results in the following mode of operation: A stream of data packets arrives at the memory device, is distributed to the logic queues on the basis of the routing information, and is temporarily stored there.
Such a facility has the advantage that the data packets are temporarily stored in different queues which can be served in different ways, and that storage utilization is better than with separate queues with fixed memory allocation. This results from the fact that all locations of the memory device can be used by all queues.
Under overload conditions, the loss proability of data packets is, as a rule, independent of their affiliation with a logic queue. In many cases, however, it is necessary for the loss probability of the data packets in a given queue to be as low as possible. For data packets of another queue which is of less importance, a slightly higher loss probability would be tolerated.